With development of electronic technology, many electronic devices such as mobile phone, personal digital assistant (PDA), tablet PC, netbook and ultrabook are widely used. While many electronic devices have to support AOAC (always on and always connected) mode, i.e., standby mode, in which an electronic device is active but draws little current. The standby time period, in another word, how long the electronic device can stay in AOAC mode is critical. As load only draws little current in AOAC mode, overall efficiency at light load is of vital importance.
Switch mode power supply is widely used in electronic devices for power conversion due to their excellent load transient response, high efficiency, small size and easy integration. But quiescent current costs most of power and mainly effects efficiency at light load.